Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a blood vessel or other anatomical lumen after implantation into the body lumen. Stents have been developed with coatings to deliver drugs or other therapeutic agents.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications including intravascular angioplasty. For example, a balloon catheter device is inflated during PTCA (percutaneous transluminal coronary angioplasty) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. After inflation, the pressurized balloon exerts a compressive force on the lesion thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels re-narrow.
To prevent restenosis, short flexible cylinders, or stents, constructed of metal or various polymers are implanted within the vessel to maintain lumen size. The stents acts as a scaffold to support the lumen in an open position. Various configurations of stents include a cylindrical tube defined by a mesh, interconnected stents or like segments. Some exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz, and U.S. Pat. No. 5,421,955 to Lau. Another exemplary wire stent is the Welded Sinusoidal Wave Stent disclosed in U.S. Pat. No. 6,136,023 to Boyle. Balloon-expandable stents are mounted on a collapsed balloon at a diameter smaller than when the stents are deployed. Stents can also be self-expanding, growing to a final diameter when deployed without mechanical assistance from a balloon or like device.
Concern over the long-term effects of stents in the body has led to renewed interest in the development of bare metal stents, i.e., stents with no polymers on their exposed surfaces. During one of the final steps of fabrication, the stents are polished to provide a smooth surface that makes the stent more biocompatible and less likely to be thrombogenic. It was discovered that a polished surface also improves the trackability of the stent, i.e., the polished surface reduces the force required to deliver a stent installed on an expansion balloon through the vasculature. Unfortunately, such a polished surface also results in poor retention of the stent on the balloon: during delivery, the stent is more likely to move from its initial position on the balloon or even become dislodged from the balloon.
It would be desirable to have a preferentially electropolished stent system and method of manufacture that would overcome the above disadvantages.